1. Field of the Invention
This invention relates to a method for stabilization of oils in water, and more particularly, to a method for preparing stable, discrete microdroplets of a high viscosity oil in water stabilized by an in situ produced water-soluble polymer solution and a surfactant.
2. Description of the Prior Art
The unique properties of many oils make it desirable to include them in aqueous-based compositions. For example, cosmetically-active materials such as silicone oils, fluids and gums, mineral oils, and water-insoluble organic esters such as isopropropyl palmitate and isopropyl myristate, are particularly useful in cosmetic formulations for the skin and hair. In such compositions, their lubricity properties impart conditioning action for the user. However, such oils are immiscible with water which makes it very difficult to maintain a stable aqueous dispersion without rapid separation of the composition into oil and water phases. To solve the problem of providing effective dispersibility of such materials in water, it has been necessary to include a surfactant in aqueous cosmetic compositions containing cosmetically-active oils in order to maintain dispersed droplets of the oil in the aqueous solution. However, even with a surfactant present, the stability of the dispersion is often not completely satisfactory, particularly where high viscosity oils are used.
Another approach is to form macroscopic capsules of an oil by in situ aqueous polymerization of oil soluble monomers. For example, Brynko, in U.S. Pat. Nos. 2,969,330 and 2,969,331, described the preparation of pressure-rupturable capsules of a chlorinated diphenyl oil in water by dissolving styrene, an acrylate or vinyl acetate monomer in the oil, dispersing the monomer-containing oil in water with the aid of an emulsifier to form droplets, and polymerizing the monomer to form an encapsulating wall of solid polymer material around each droplet of oil.
Berg, in J. Microencapsulation (1989) 6, No. 3, 327-337, also described a process for the microencapsulation of emulsified oil droplets by in situ vinyl polymerization. However, the process was limited to the use of methyl methacrylate, an oil soluble monomer, to form a polymer shell around emulsified oil droplets of decane and hexadecane.
De Luca, in U.S. Pat. No. 4,741,872, described the preparation of biodegradable microspheres having a three-dimensional network in which biologically active macromolecular agents were physically entrapped therein. The method involved emulsifying a vinyl derivative of a biodegradable hydrophilic polymer, a water-soluble monovinyl monomer, and a biologically active macromolecular agent, in water, and copolymerizing the vinyl compounds.
However, these and other processes have not provided a method by which cosmetically active oils, such as silicone oils, can be prepared as a stable dispersion in an aqueous medium. Nor does the prior art suggest a procedure for allowing oils of high viscosity to maintain themselves effectively in stable condition in an aqueous cosmetic formulation.
Accordingly, it is an object of the present invention to provide a process for stabilizing oils in water, preferably in the form of microdroplets, maintained discretely and for an extended period of time in an aqueous medium.
Another object of this invention is to provide a method for preparing an aqueous composition which includes stable, discrete microdroplets of an oil, including an oil of high viscosity, dispersed therein.
Still another object of the present invention is to provide a method of preparing a composition in which microdroplets of oils of high viscosity are homogeneously distributed in the composition.
Yet another object is to provide such stable, dispersed microdroplets by in situ polymerization of a water-soluble vinyl monomer, such as vinylpyrrolidone, in the presence of dispersed droplets of a water-insoluble oil, such as silicone oil, including high viscosity oils, in water containing a surfactant.
Among the other objects of the invention is to provide a cosmetic formulation containing stable, discrete microdroplets of a cosmetically-active oil stabilized in an aqueous solution in situ polymerized vinylpyrrolidone.
These and other objects and features of the invention will be made apparent from the following description thereof.